1. Field of the Invention
The present invention generally relates to voice and data communication systems. More particularly, this invention relates to wireless communication systems including conversion between frequency bands.
2. Description of the Related Art
Over the last decade, the deployment of wireless communication systems around the world has been phenomenal. Wireless communication technology has evolved along a logical path, from simple first-generation analog systems designed for business use to second-generation digital wireless communication systems for business and personal applications.
The first-generation analog systems include the Advanced Mobile Phone System (AMPS). The AMPS system is the widely used system in the United States. It uses cellular analog technology, now defined by the Electronics Industries Alliance (xe2x80x9cEIAxe2x80x9d) specification EIA-553. The term xe2x80x9ccellularxe2x80x9d refers to dividing the service area into many small regions, called cells, each served by a low-power transmitter. Analog systems typically use analog frequency modulation (FM) for speech transmission and frequency shift keying (FSK) for signalling (i.e., control messages). In the United States, the AMPS uses frequency ranges of 824-849 MHz for mobile station transmissions (uplink), and 869-894 MHz for base stations transmissions (downlink). Additionally, a narrowband AMPS (N-AMPS) has also been deployed to increase capacity. N-AMPS divides an analog channel into three parts, thereby tripling the present analog channel capacity.
Outside the United States, there are two main international standards employing digital technology. These standards are the Global System for Mobile Communications (GSM/DCS-1800), and Japanese Digital Cellular (JDC). In the United States, the second generation digital wireless systems conform with the EIA IS-54 or IS-95 digital system standards. The EIA IS-54 standard employs time division multiple access (TDMA), and IS-95 employs code division multiple access (CDMA). Other systems conforming to the IS-136 (employing TDMA) and Personal Communications Services (PCS) standards are also now deployed in the United States.
Systems employing PCS technology operate in the frequency range 1850-1910 MHz for the uplink (i.e., mobile transmit, base receive) and 1930-1990 MHz for the downlink (i.e., base transmit, mobile receive). There are currently two communication standards operating in the PCS bands: a GSM-equivalent standard which employs a combination of TDMA and frequency division multiple access (FDMA), and a spreadspectrum standard employing code division multiple access (CDMA). Using TDMA, the users share the radio spectrum in the time domain. A user is allocated a time slot during which either the whole frequency band (wideband TDMA) or only a part of the band (narrowband TDMA) is accessed. Using FDMA, the users share the radio spectrum in the frequency domain. A user is allocated at least one unique frequency for communication without interference with users in the same frequency spectrum. Using CDMA, a transmitted signal is spread over a band of frequencies much wider than the minimum bandwidth required to transmit the signal.
PCS systems enable users to efficiently transfer any form of information between any desired locations. Basic needs for PCS include standardized low-power technology to provide voice and data to small, economical, pocket-size personal handsets. With other competitive systems already in place, PCS providers are tasked with finding creative ways of providing extensive service to their customers. To provide extensive coverage, however, PCS providers are confronted with a high equipment cost to provide additional cells. Additionally, government-imposed regulations on service providers may increase these costs if new virtual cells are not added within mandated deadlines.
To combat these problems, PCS providers have used repeaters to extend cell coverage area at its edge or fill-in dead spots within the cell. xe2x80x9cDead spotsxe2x80x9d are areas which have weak reception due to geographic barriers or RF interference. A repeater is a bi-directional radio frequency (RF) amplifier system which receives RF signals from a base transceiver station (BTS) of a donor cell, amplifies the RF signals and retransmits them to subscribers. A xe2x80x9cdonor cellxe2x80x9d is the cell from which a repeater receives RF signals for further transmission. Conventional repeaters have been designed to operate in fringe areas (i.e., zones just outside the range of a BTS in which RF signals are weak).
One limitation of conventional repeaters is that they can only operate within the neighborhood of the donor cell, where RF coverage is inadequate. In certain situations, coverage may be required tens of miles away from the nearest BTS. To meet this demand, repeaters are cascaded, i.e., placed in geographic sequence, to further extend the coverage area of a BTS. However, cascading conventional repeaters to perform this task can be expensive and time consuming. More importantly, there are technical complications associated with cascading repeaters. One major complication is the associated overall time delay due to sequential repeaters, thereby limiting the maximum number of repeaters that can be cascaded without significant signal degradation.
In view of the foregoing, there is a need in the industry for a new repeater system which extends the coverage area in a wireless communication system without the disadvantages of conventional repeaters. The new repeater system should enable expansion of coverage areas without imposing time-delay or intra-band interference. This repeater system should expand coverage areas while maintaining minimal channel inter-cell interference or congestion. Furthermore, such system should be easy to install and maintain.
To overcome the above problems, the present invention provides a repeater system which allows the expansion of existing mobile communications coverage areas without the disadvantages of the prior art. The above-mentioned problems are solved by providing an inter-band repeater system which provides conversion of communication from cellular/mobile frequency bands to other frequency bands, such as the Industrial, Scientific and Medical (ISM) frequency bands. The ISM frequency bands allocated by the Federal Communications Commission (FCC) are spread across the frequency ranges of 902-928 MHz, 2400-2484 MHz, and 5725-5850 MHz. The repeater system provides full duplex communications while maintaining proper signalling schemes for a variety of wireless communication systems, such as mobile systems employing CDMA, TDMA, E-TDMA, FDMA, frequency hopping, or similar technologies.
In accordance with one embodiment of the present invention, the repeater system converts PCS signals to ISM frequency bands. The repeater system comprises two main substations: a near-end ISM band transceiver (the xe2x80x9cNEITxe2x80x9d station) and a farend ISM band transceiver (the xe2x80x9cFEITxe2x80x9d station). In one direction, called the forward link, the NEIT station receives PCS signals from a BTS of a donor cell, converts the carrier frequencies of the PCS signals to ISM frequencies, and transmits these signals using an antenna over ISM bands. The FEIT station receives these signals, converts the carrier frequencies of these signals to PCS frequencies, and transmits the PCS signals at the desired location. In effect, a new virtual cell is created at the desired location using the FEIT station of the repeater system. The repeater system implements all these steps without affecting signal quality. More importantly, the repeater system processes the PCS signals without interference with the signal modulation and schemes.
The repeater system supports full-duplex communication between a donor cell and a new virtual cell. Hence, the operation of the repeater system in the opposite direction, called the reverse link, is similar to that of the forward link. The PCS signal is preferably received by the BTS of the donor cell and re-transmitted by that BTS.